Photochromism is a reversible phenomenon illustrated by a compound which, upon exposure to the radiation of light including ultraviolet rays, such as sunlight or the light of a mercury lamp, changes color and then returns to its original color if the radiation is discontinued or the compound is stored in the dark. A compound illustrating this phenomenon is called a "photochromic compound."
Spiro(indoline) type compounds, e.g., spiro[indoline-pyran]- and spiro[indoline-oxazine]-type compounds, have been described as possessing photochromic properties and have been suggested for use in applications in which a color change induced by sunlight is desired. For example, spiro[indoline-naphthoxazine] compounds are described in European Patent Application No. 171909 and in U.S. Pat. Nos. 3,562,172, 3,578,602, 4,215,010 and 4,342,668. Such spiro[indoline-naphthoxazine] compounds can be readily produced by the condensation reaction of an alkylidene heterocyclic compound, e.g., a Fischer's Base reactant, such as a substituted 2-methyleneindoline compound, and an ortho-nitroso-hydroxynaphthalene. Similarly, while spiro[indoline-pyran]-type compounds, such as spiro[indoline-benzopyran] or spiro[indoline-naphthopyran], can be produced respectively by the condensation reaction of a Fischer's base reactant and ortho hydroxyl formyl benzene or 1-formyl-2-hydroxylnaphthalene, efforts to obtain spiro[indoline-benzoxazine] compounds by the condensation reaction of a Fischer's base reactant and an ortho-nitrosophenol have been less successful. This lead to the search for an alternative synthetic route to compounds such as the spiro(indoline)benzoxazines.